Ubuntu 18.04 defaults to using a swap file instead of the previous method of having a dedicated swap partition. This makes it easier to partition new installations of 18.04 than it was before.
Assuming you are going to do a fresh installation of 18.04, and also assuming you aren't trying to dual-boot with this same drive, here's what you should do:
Boot to a Ubuntu 18.04 installer (probably using a usb drive)
Delete the three existing partitions from your hard drive: /dev/sda1, /dev/sda2, and /dev/sda3.
Create one new partition, /dev/sda1, that uses all the available space. Make the new partition primary (not extended), format it as ext4, and have it mount the root of the system (/).
Install ubuntu, selecting to put the bootloader on /dev/sda